Distributor Q?
 

The TDC mark on my distributor is located on the back and not the front like the diagrams in the manual and on the engine bay shows.

Will this create an issue if I use that point for cylinder #1 and still follow the same firing order? The engine is set at TDC with the rotor pointing at the notch.

Or should I re index the dizzy so it points to the front, and guess where the mark should be?

Its a 79 930 USA version

As long as the rotor points to the correct cylinder when it's ready to fire, no problem. Is there enough room to rotate the distributor w/o the vacuum unit blocking movement?

Even tough it's okay, one shouldn't have too many workarounds. If your vehicle is in the care of a repair shop, they will appreciate some resemblance to the way the factory assembled the engine.

If you want to reindex the distributor, here's how:
1. Rotate engine so rotor points to current number one plug wire on dist. cap.
2. Mark crank with chalk relative to the crankcase split.
3. Remove or elevate the distributor in its housing so the driven gear disengages from the drive gear.
4. Rotate crankshaft 1 revolution in the direction of normal rotation.
5. Reinstall distributor so the rotor points 180º from its previous position in step 1.
6. Remove and replace all plug wire positions on dist. cap 3 positions. Number 1 plug wire should now be 180º from previous position and opposite the rotor. Make sure the firing order is in the correct sequence.
7. Start engine and set ignition timing to specs.

Hope this helps,
Sherwood